High Strength Polyisobutylene Polyurethanes

ABSTRACT

An elastomeric polymer, comprising (1) a hard segment in the amount of 10% to 60% by weight of the elastomeric polymer, wherein the hard segment includes a urethane, urea, or urethaneurea; and (2) a soft segment in the amount of 40% to 90% by weight of the elastomeric polymer, wherein the soft segment includes a polyisobutylene macrodiol and/or diamine. Additionally disclosed is a method of forming a polyisobutylene-based thermoplastic urethane, comprising the steps of (a) reacting a polyisobutylene macrodiol and/or diamine with a diisocyanate to form a first reaction mixture; (b) combining a metal catalyst and a chain extender with the first reaction mixture to create a second reaction mixture, a molar ratio of the metal catalyst to the diisocyanate being greater than 0.0:1 and less than or equal to 0.4:1; and (c) reacting the second reaction mixture for a period of time sufficient to form the polyisobutylene-based thermoplastic urethane.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/433,974, filed on Apr. 7, 2015, which is the U.S. National Stage ofInternational Application No. PCT/US2013/071170, filed Nov. 21, 2013,which designates the U.S., published in English, which claims thebenefit of U.S. Provisional Application No. 61/729,124, filed Nov. 21,2012; and U.S. Provisional Application 61/819,285, filed May 3, 2013.The entire teachings of the above applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

Thermoplastic polyurethanes, polyureas, and polyurethaneureas representan important family of segmented block copolymer thermoplasticelastomers. They can be extruded, injection or compression molded, orsolution spun. They offer a broad range of physical properties andcharacteristics, including high tensile and tear strength, chemical andabrasion resistance, good processability, and protective barrierproperties. Polyurethanes are the most commonly used materials in theproduction of biomedical devices that come in contact with blood such aspacemakers, defibrillators, angioplasty balloons, surgical drains,dialysis devices, etc.

Depending on composition, i.e. on the volume fraction of the soft,elastomeric segments, these polymers can be soft and rubbery, or hardand rigid materials. The hard segments of polyurethanes or polyureas arecomposed of diisocyanate and a small molecule diol or diamine chainextender. These hard segments may comprise, for example, diamines and acombination of diols and diamines, respectively, in addition todiisocyanate. The soft segments are mostly low molecular weightpolymeric diols, which may include polyester diols, polyether diols, andpolydiene diols.

Polyurethanes that incorporate a polyether diol into the soft segmentgenerally suffer long-term in vivo bioinstability due to oxidation ofthe polyether soft segment, especially when in contact with metals,which catalyze oxidative degradation. This deficiency limits the use ofpolyurethanes for long-term applications.

Polyisobutylene (PIB)-based thermoplastic polyurethanes (TPUs) offerhigh thermal, oxidative, and hydrolytic stability, but exhibitinsufficient mechanical properties without the addition of a polyetheror polyester diol. The need for a PIB-based TPU that exhibits sufficientmechanical properties and biostability is still present.

SUMMARY OF THE INVENTION

It has now been discovered that the mechanical properties of PIB-basedTPUs are highly affected by the catalyst concentration present duringsynthesis. Specifically, utilization of a specific range of catalystconcentration yields PIB-based TPUs with substantially improvedmechanical strength.

In an example embodiment, the present invention is an elastomericpolymer comprising a hard segment and a soft segment. The hard segmentis present in the amount of 10% to 60% by weight of the elastomericpolymer, wherein the hard segment includes a urethane, urea, orurethaneurea. The soft segment is present in the amount of 40% to 90% byweight of the elastomeric polymer, wherein the soft segment includes apolyisobutylene macrodiol and/or diamine and does not include apolyether macrodiol. The number average molecular weight of theelastomeric polymer is greater than or equal to 40 kilodaltons, and thepolydiversity index of the hard segment is between 1.58 and 2.17,inclusive.

In another embodiment, the present invention is a method of forming apolyisobutylene-based thermoplastic urethane, comprising the steps of:reacting a polyisobutylene macrodiol and/or diamine with a diisocyanateto form a first reaction mixture; combining a metal catalyst and a chainextender with the first reaction mixture to create a second reactionmixture, a molar ratio of the metal catalyst to the diisocyanate beinggreater than 0.0:1 and less than or equal to 0.4:1; and reacting thesecond reaction mixture for a period of time sufficient to form thepolyisobutylene-based thermoplastic urethane.

In another embodiment, a polyisobutylene-based thermoplastic urethane isformed by a method comprising the steps of: reacting a polyisobutylenediol with a diisocyanate to form a reaction mixture; combining ametal-catalyst of an alkyl diol with the reaction mixture, a molar ratiox of elemental metal of the metal-catalyst to diisocyanate being in arange of 0.0:1<x<0.4:1; and reacting the reaction mixture with themetal-catalyst of alkyl diol for a period of time sufficient to form thepolyisobutylene-based thermoplastic urethane.

The polyisobutylene-based thermoplastic polyurethanes of the presentinvention can be used to manufacture elastomeric materials useful in theproduction of biomedical devices, surgical drains, dialysis devices,etc. The polyisobutylene-based thermoplastic materials of the presentinvention present a number of advantages over previously disclosedmaterial. Specifically, these polyisobutylene-based thermoplasticmaterials do not rely on a polyether or polyester macrodiol to achievesufficient mechanical properties. Without a polyether or polyester diolstructure present in the polymer structure, the polyisobutylene-basedthermoplastic materials of the present invention do not suffer the samebioinstability against hydrolytic and oxidative degradations thataffected previously disclosed polyisobutylene-based thermoplastics.

The polyisobutylene-based thermoplastics of the present inventionexhibit improved tensile strength and percent elongation beyond what waspreviously known without a polyether or polyester diol. By controllingthe catalyst concentration, a polyisobutylene-based thermoplasticmaterial with mechanical properties comparable to polyether or polyestermacrodiol-containing polyisobutylene-based thermoplastic materials canbe synthesized. These improved mechanical properties are attributed to anarrower molecular weight distribution (MWD) of the hard segments.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments of the present invention.

FIG. 1 is a plot of heat flow (mW) vs. Temperature (° C.).

FIG. 2A is a plot of loss modulus (E″) vs. Temperature (° C.).

FIG. 2B is a plot of tan δ vs. Temperature (° C.).

FIG. 3A is a plot of I(cm⁻¹) vs. q(nm⁻¹).

FIG. 3B is a plot of q²I(q)(10¹⁴ cm⁻³) vs. q(nm⁻¹).

FIG. 4A is a plot of I(cm⁻¹) vs. q(nm⁻¹).

FIG. 4B is a plot of q²I(q)(10¹⁴ cm⁻³) vs. q(nm⁻¹).

FIG. 5 is an illustration that represents example structuralconformations PIB-based TPUs may form based on catalyst concentration.

FIG. 6 is a plot of Tensile Stress (MPa) vs. Elongation (%).

FIG. 7 is a plot of the elution time (min) of PIB(OH)₂-based TPU beforeand after attempted oxidation.

FIG. 8 is a plot of the elution time (min) of PIB(allyl-OH)₂ overlaid onthe elution time of cleaved PIB(allyl-OH)₂-based TPU.

FIG. 9 is a plot of the elution time (min) of the hard segment ofcleaved PIB(allyl-OH)₂-based TPU.

DETAILED DESCRIPTION OF THE INVENTION Glossary

As used herein, the term “molecular weight distribution” (MWD) refers tothe distribution of molecular weight among polymer molecules in a givenpolymer sample. The MWD is expressed as a plot, wherein the x-axismeasures the molecular weight of a polymer sample, and the y-axismeasures the number of polymer molecules with that correspondingmolecular weight. A narrow curve corresponds to a uniform distributionof weight among polymer molecules in a given polymer sample.

As used herein, the term “polydispersity index” (PDI) also refers to thedistribution of molecular weight among polymer molecules in a givenpolymer sample. The PDI calculated is the weight average molecularweight divided by the number average molecular weight. PDI may be usedas a measure of MWD. A PDI that approaches the value of 1 represents auniform distribution of weight among polymer molecules in a givenpolymer sample.

As used herein, the term “M_(n)” refers to the number average molecularweight of a given polymer sample.

As used herein, the term “M_(w)” refers to the weight average molecularweight of a given polymer sample.

As used herein, the term “macrodiol” means a polymeric diol. Examplesinclude polyether compounds of the formula

HO—[CH(R)—(CH₂)_(k)—O]_(l)—H,   (I)

and polyisobutylene polymers of the formula

values and preferred values for the variables in formulas (I) and (II)are defined below.

Similarly, when the phrase “macrodiol and/or diamine” is used, thereference is being made to a polymeric diamine similar in structure tothe diols of formulas (I) and (II), in which the terminal hydroxylgroups are replaced with amino or alkylamino groups, as defined below.

As used herein, the term “telechelic,” when referring to a polymer,means a polymer carrying functionalized endgroups. Examples oftelechelic polymers are difunctional polymers of formula (II), above.Telechelic polymers can be used, e.g., for the synthesis of blockco-polymers.

As used herein, the term “BDO” refers to 1,4-butanediol.

As used herein, the term “MDI” refers to4,4′-methylenebis(phenylisocyanate).

As used herein, the term “PIB” means a polyisobutylene, i.e. a compoundformed by a polymerization of isobutylene.

As used herein, the term “TPU” means a thermoplastic polyurethane.

As used herein, the term “PIB-TPU” means a polyisobutylene-basedthermoplastic polyurethane obtained by any known process. The termincludes the elastomeric polyurethanes materials described herein.

As used herein, the term “initiator residue” refers to a difunctionalchemical moiety that links two linear chains of a polymer. For example,in a polyisobutylene polymer of the formula

where values and preferred values are defined below, R₁ is an initiatorresidue. Examples of initiator residues include dicumyl and5-tert-butyl-1,3 dicumyl that correspond to dicumyl chloride,methylether or ester, respectively, are used as initiator. Otherexamples include 2,4,4,6-tetramethylheptylene or 2,5-dimethylhexylene,which arise when 2,6-dichloro-2,4,4,6-tetramethylheptane or2,5-dichloro-2,5-dimethylhexane is used as an initiator. Many othercationic mono- and multifunctional initiators are known in the art.

The term “alkyl,” as used herein, unless otherwise indicated, meansstraight or branched saturated monovalent hydrocarbon radicals offormula C_(n)H_(2n+1). In some embodiments, n is from 1 to 18. In otherembodiments, n is from 1 to 12. Preferably, n is from 1 to 6. In someembodiments, n is 1 to 1000. Alkyl can optionally be substituted with—OH, —SH, halogen, amino, cyano, nitro, a C₁-C₁₂ alkyl, C₁-C₁₂haloalkyl, C₁-C₁₂ alkoxy, C₁-C₁₂ haloalkoxy, or C₁-C₁₂ alkyl sulfanyl.In some embodiments, alkyl can optionally be substituted with one ormore halogen, hydroxyl, C₁-C₁₂ alkyl, C₁-C₁₂ alkenyl or C₁-C₁₂ alkynylgroup, C₁-C₁₂ alkoxy, or C₁-C₁₂ haloalkyl. The term alkyl can also referto cycloalkyl.

The term “alkenyl,” as used herein, includes the alkyl moieties asdefined above, having at least one carbon-carbon double bond. In someembodiments, alkenyl groups have from 2 to 18 carbon atoms. In otherembodiments, alkenyl groups have from 2 to 12 carbon atoms. Preferably,alkenyl groups have from 2 to 6 carbon atoms. Examples of alkenyl groupsinclude ethenyl (—CH═CH₂), n-2-propenyl (allyl, —CH₂CH═CH₂), pentenyl,hexenyl, and the like. The term alkenyl can also refer to cycloalkenyl.

The term “alkynyl,” as used herein, includes the alkyl moieties asdefined above, having at least one carbon-carbon triple bond. In someembodiments, alkynyl groups have from 2 to 18 carbons. In otherembodiments, alkynyl groups have from 2 to 12 carbon atoms. Preferably,alkynyl groups have from 2 to 6 carbon atoms. Examples of alkynyl groupsinclude ethynyl (—C≡CH), propargyl (—CH₂C≡CH), pentynyl, hexynyl, andthe like. The term alkynyl can also refer to cycloalkynyl.

The term “cycloalkyl”, as used herein, means saturated cyclichydrocarbons, i.e. compounds where all ring atoms are carbons. In someembodiments, a cycloalkyl comprises from 3 to 18 carbons. Preferably, acycloalkyl comprises from 3 to 6 carbons. Examples of cycloalkylinclude, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, and cycloheptyl. In some embodiments, cycloalkyl canoptionally be substituted with one or more halogen, hydroxyl, C₁-C₁₂alkyl, C₁-C₁₂ alkenyl or C₁-C₁₂ alkynyl group, C₁-C₁₂ alkoxy, or C₁-C₁₂haloalkyl.

The term “haloalkyl,” as used herein, includes an alkyl substituted withone or more F, Cl, Br, or I, wherein alkyl is defined above.

The terms “alkoxy,” as used herein, means an “alkyl-O—” group, whereinalkyl is defined above. Examples of alkoxy group include methoxy orethoxy groups.

The term “aryl,” as used herein, refers to a carbocyclic aromatic group.Preferably, an aryl comprises from 6 to 18 carbons. Examples of arylgroups include, but are not limited to phenyl and naphthyl. Examples ofaryl groups include optionally substituted groups such as phenyl,biphenyl, naphthyl, phenanthryl, anthracenyl, pyrenyl, fluoranthyl orfluorenyl. An aryl can be optionally substituted. Examples of suitablesubstituents on an aryl include halogen, hydroxyl, C₁-C₁₂ alkyl, C₁-C₁₂alkene or C₁-C₁₂ alkyne, C₃-C₁₂ cycloalkyl, C₁-C₁₂ haloalkyl, C₁-C₁₂alkoxy, aryloxy, arylamino, or aryl group.

The term “aryloxy,” as used herein, means an “aryl-O—” group, whereinaryl is defined above. Examples of an aryloxy group include phenoxy ornaphthoxy groups.

The term “amino,” as used herein, means an “—NH₂,” an “NHR_(p),” or an“NR_(p)R_(q),” group, wherein R_(p) and R_(q) may be any of the alkyl,alkenyl, alkynyl, alkoxy, cycloalkyl, cycloalkoxy, aryl, heteroaryl, andbicyclic carbocyclic groups. In the present invention, the amino may beprimary (NH₂), secondary (NHR_(p)) or tertiary (NR_(p)R_(q)). Adialkylamino group is an instance of an amino group substituted with oneor two alkyls. A trialkylamino group is a group —N⁺(R_(t))₃, whereinR_(t) is an alkyl, as defined above.

The term “arylamine,” as used herein, means an “aryl-NH—,” an“aryl-N(alkyl)-,” or an “(aryl)₂-N—” group, wherein aryl and alkyl aredefined above.

The term “heteroaryl,” as used herein, refers to aromatic groupscontaining one or more heteroatoms (O, S, or N). A heteroaryl group canbe monocyclic or polycyclic, e.g., a monocyclic heteroaryl ring fused toone or more carbocyclic aromatic groups or other monocyclic heteroarylgroups. The heteroaryl groups of this invention can also include ringsystems substituted with one or more oxo moieties. Examples ofheteroaryl groups include, but are not limited to, pyridinyl,pyridazinyl, imidazolyl, pyrimidinyl, pyrazolyl, triazolyl, pyrazinyl,quinolyl, isoquinolyl, tetrazolyl, furyl, thienyl, isoxazolyl,thiazolyl, oxazolyl, isothiazolyl, pyrrolyl, quinolinyl, isoquinolinyl,indolyl, benzimidazolyl, benzofuranyl, cinnolinyl, indazolyl,indolizinyl, phthalazinyl, pyridazinyl, triazinyl, isoindolyl, purinyl,oxadiazolyl, thiazolyl, thiadiazolyl, furazanyl, benzofurazanyl,benzothiophenyl, benzotriazolyl, benzothiazolyl, benzoxazolyl,quinazolinyl, quinoxalinyl, naphthyridinyl, dihydroquinolyl,tetrahydroquinolyl, dihydroisoquinolyl, tetrahydroisoquinolyl,benzofuryl, furopyridinyl, pyrolopyrimidinyl, and azaindolyl.

The foregoing heteroaryl groups may be C-attached or N-attached (wheresuch is possible). For instance, a group derived from pyrrole may bepyrrol-1-yl (N-attached) or pyrrol-3-yl (C-attached).

Suitable substituents for heteroaryl are as defined above with respectto aryl group.

Suitable substituents for an alkyl or cycloalkyl include a halogen, analkyl, an alkenyl, a cycloalkyl, a cycloalkenyl, an aryl, a heteroaryl,a haloalkyl, cyano, nitro, haloalkoxy.

Further examples of suitable substituents for a substitutable carbonatom in an aryl, a heteroaryl, alkyl or cycloalkyl include but are notlimited to —OH, halogen (F, Cl, Br, and I), —R, —OR, —CH₂R, —CH₂OR,—CH₂CH₂OR. Each R is independently an alkyl group.

In some embodiments, suitable substituents for a substitutable carbonatom in an aryl, a heteroaryl or an aryl portion of an arylalkenylinclude halogen, hydroxyl, C₁-C₁₂ alkyl, C₁-C₁₂ alkenyl or C₁-C₁₂alkynyl group, C₁-C₁₂ alkoxy, aryloxy group, arylamino group, and C₁-C₁₂haloalkyl.

In addition, the above-mentioned groups may also be substituted with ═O,═S, ═N— alkyl.

Polyurethanes and Polyureas

As used herein, “polyurethane” is any polymer consisting of a chain oforganic units joined by urethane (carbamate, —NH—COO—) links.Polyurethane polymers can be formed by reacting a molecule containing atleast two isocyanate functional groups with another molecule containingat least two alcohol (hydroxyl) groups. By reacting an isocyanate group,—N═C═O, with a hydroxyl group, —OH, a urethane linkage is produced. Acatalyst can be used. Similarly, in polyureas the links are urea groups(NH—CO—NH—) that are obtained by reacting an isocyanate group with anamine group —NH2.

For example, polyurethanes can be produced by the polyaddition reactionof a polyisocyanate with a polyalcohol (a polyol, an example of which isa macrodiol). The reaction mixture can include other additives. Apolyisocyanate is a molecule with two or more isocyanate functionalgroups, R₁—(N═C═O)_(n≥2), and a polyol is a molecule with two or morehydroxyl functional groups, R₂—(OH)_(n≥2). R₁ and R₂ are eachindependently an aliphatic or an aromatic moiety. The reaction productis a polymer containing the urethane linkage, —R₁NHCOOR₂—.

Polyisocyanates that contain two isocyanate groups are calleddiisocyanates. Isocyanates can be aromatic, such as diphenylmethanediisocyanate (MDI) or toluene diisocyanate (TDI); or aliphatic, such ashexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI). Anexample of an isocyanate is polymeric diphenylmethane diisocyanate,which is a blend of molecules with two-, three-, and four- or moreisocyanate groups, with an average functionality of 2.7.

Polyols that contain two hydroxyl groups are called macrodiols, thosewith three hydroxyl groups are called macrotriols. Examples of polyolsinclude polycarbonate polyols, polycaprolactone polyols, polybutadienepolyols, and polysulfide polyols.

Additives such as catalysts, surfactants, blowing agents, cross linkers,flame retardants, light stabilizers, and fillers are used to control andmodify the reaction process and performance characteristics of thepolymer.

Examples of aromatic isocyanates are toluene diisocyanate (TDI) anddiphenylmethane diisocyanate (MDI). TDI consists of a mixture of the2,4- and 2,6-diisocyanatotoluene isomers. Another example of an aromaticisocyanate is TDI-80, consisting of 80% of the 2,4-isomer and 20% of the2,6-isomer.

Examples of aliphatic (including cycloaliphatic) isocyanates are1,6-hexamethylene diisocyanate (HDI),1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophoronediisocyanate, IPDI), and 4,4′-diisocyanato dicyclohexylmethane (H₁₂MDI).Other aliphatic isocyanates include cyclohexane diisocyanate (CHDI),tetramethylxylene diisocyanate (TMXDI), and1,3-bis(isocyanatomethyl)cyclohexane (H₆XDI).

Chain extenders (f=2) and cross linkers (f=3 or greater) are lowmolecular weight hydroxyl and amine terminated compounds that play animportant role in the polymer morphology of polyurethane fibers,elastomers, adhesives, and certain integral skin and microcellularfoams. Examples of chain extenders and cross linkers are ethylene glycol(EG), 1,4-butanediol (BDO), diethylene glycol (DEG), glycerine, andtrimethylol propane (TMP).

The elastomeric properties of polyurethanes, polyureas andpolyurethaneureas are derived from the phase separation of the “hardsegment” and the “soft segment” domains of the polymer chain. Forexample, hard segments that comprise urethane units can serve ascross-links between the soft segments that comprise polyol (e.g.,macrodiol) units (e.g., polyisobutane diols). Without being limited toany particular theory, it is believed that the phase separation occursbecause the mainly non-polar, low melting soft segments are incompatiblewith the polar, high melting hard segments. The polyol-containing softsegments are mobile and are normally present in coiled formation, whilethe isocyanate-containing hard segments (which can also include chainextenders) are stiff and immobile. Because the hard segments arecovalently coupled to the soft segments, they inhibit plastic flow ofthe polymer chains, thus creating elastomeric resiliency. Uponmechanical deformation, a portion of the soft segments are stressed byuncoiling, and the hard segments become aligned in the stress direction.This reorientation of the hard segments and consequent powerful hydrogenbonding contributes to high tensile strength, elongation, and tearresistance values.

Although the synthesis of polyurethanes is usually presented asproceeding via formation of urethane (carbamate) linkages by thereaction of isocyanates and alcohols, this is an oversimplification.See, for example, G. ODIAN: PRINCIPLES OF POLYMERIZATION, FOURTH ED.Wiley Interscience, 2004. Accordingly, it is more convenient to definethe polyurethane compositions via weight percent of the componentsrather than structurally.

Accordingly, in an example embodiment, the present invention is anelastomeric polymer, comprising (1) a hard segment in the amount of 10%to 60% by weight of the elastomeric polymer, wherein the hard segmentincludes a urethane, urea or urethaneurea; and (2) a soft segment in theamount of 40% to 90% by weight of the elastomeric polymer, wherein thesoft segment includes a polyisobutylene macrodiol and/or diamine anddoes not include a polyether macrodiol.

In another embodiment, the number average molecular weight of theelastomeric polymer is greater than or equal to about 40 kilodaltons(kDa). In other embodiments, the number average molecular weight of theelastomeric polymer is greater than or equal to about 50 kDa. Inalternative embodiments, wherein the number average molecular weight ofthe elastomeric polymer is greater than or equal to about 60 kDa,greater than or equal to about 70 kDa, greater than or equal to about 80kDa, greater than or equal to about 90 kDa, greater than or equal toabout 100 kDa, greater than or equal to about 110 kDa, greater than orequal to about 120 kDa, greater than or equal to about 130 kDa, greaterthan or equal to about 140 kDa, or greater than or equal to about 150kDa.

In another embodiment, the hard segment can be present in the amount of15, 20, 25, 30, 35, 40, 45, 50, or 55%.

In another embodiment, the soft segment can be present in the amount of45, 50, 55, 60, 65, 70, 75, 80, or 85%.

In another embodiment, the polydiversity index of the hard segment canbe greater than or equal to 1.58 and less than or equal to 2.17.

In another embodiment, the soft segment consists essentially ofpolyisobutylene macrodiol and/or diamine.

One of ordinary skill can easily determine a suitable polyethermacrodiol. Preferably, at least one polyether macrodiol is a compound offormula

HO—[CH(R)—(CH₂)_(k)—O]_(l)—H,

wherein R, for each occurrence, is independently a C₁-C₁₂ alkyl, or —H;k is an integer not less than 1, and l is an integer not less than 1.

One of ordinary skill can easily determine a suitable polyisobutylenemacrodiol or diamine. Preferably, at least one polyisobutylene macrodioland/or diamine is of formula:

wherein each X is independently —OH, —NH₂, or —NHR₄. R₁ is an initiatorresidue. R₂, R₃, and R₄ is, each independently, a C₁-C₁₆ alkyl, a C₃-C₁₆cycloalkyl, a C₂-C₁₆ alkenyl, a C₃-C₁₆ cycloalkenyl, a C₂-C₁₆ alkynyl, aC₃-C₁₆ cycloalkynyl, or a C₆-C₁₈ aryl, wherein, for each occurrence, R₂or R₃ is, independently, optionally substituted with one or more groupsselected from halo, cyano, nitro, dialkylamino, trialkylamino, C₁-C₁₆alkoxy, and C₁-C₁₆ haloalkyl. Variables n and m are each, independently,integers from 1 to 500.

In another embodiment, the polyisobutylene macrodiol can be hydroxyallyltelechelic polyisobutylene or hydroxyalkyl telechelic polyisobutylene.For example, the polyisobutylene macrodiol can be hydroxypropyltelechelic polyisobutylene.

In another embodiment, the polyisobutylene macrodiamine can beaminoallyl telechelic polyisobutylene.

In another embodiment, the molecular weight of at least onepolyisobutylene macrodiol or diamine is about 400 Da to about 6000 Da.For example, the molecular weight of at least one polyisobutylenemacrodiol or diamine can be about 500, 1000, 2000, 3000, 4000, or 5000Da. In certain embodiments, the molecular weight of at least onepolyisobutylene macrodiol or diamine is about 1000 Da to about 3000 Da.For example, the molecular weight of at least one polyisobutylenemacrodiol or diamine can be about 1000, 1500, 2000, or 2500 Da.

In a preferred embodiment, R₂ and R₃ is, each independently, a moietyselected from the group consisting of —CH₂—CH═CH—CH₂—;—CH₂—CH₂—CH₂—CH₂—; —CH₂—CH₂—CH₂—; and —CH₂—CH(CH₃)—CH₂—.

In another embodiment, the elastomeric polymer of the present inventioncomprises a hard segment present in the amount of from about 30% toabout 50% by weight of the elastomeric polymer. For example, the hardsegment can be present in the amount of 35, 40, or 45%.

Examples of the hard segments include the hard segments which are aproduct of reacting a diisocyanate with a chain extender. One ofordinary skill in the art will easily determine a suitable diisocyanateor a chain extender.

The diisocyanate can be at least one member selected from the groupconsisting of 4,4′-methylenephenyl diisocyanate; methylene diisocyanate;p-phenylene diisocyanate; cis-cyclohexane-1,4-diisocyanate;trans-cyclohexane-1,4-diisocyanate; a mixture ofcis-cyclohexane-1,4-diisocyanate and trans-cyclohexane-1,4-diisocyanate;1,6-hexamethylene diisocyanate; 2,4-toluene diisocyanate;cis-2,4-toluene diisocyanate; trans-2,4-toluene diisocyanate; a mixtureof cis-2,4-toluene diisocyanate and trans-2,4-toluene diisocyanate;p-tetramethylxylene diisocyanate; and m-tetramethylxylene diisocyanate.

The chain extender may be a C₂-C₁₂ alkyl diol or a C₂-C₁₂ alkyl diamine.

The chain extender may also be at least one member selected from thegroup consisting of 1,4-butanediol; 1,5 pentanediol; 1,6-hexanediol;1,8-octanediol; 1,9-nonanediol; 1,10-decanediol, 1,12-dodacanediol;1,4-cyclohexane dimethanol; p-xyleneglycol; and 1,4-bis(2-hydroxyethoxy)benzene.

Alternatively, the chain extender may be at least one member selectedfrom the group consisting of 1,4-diaminobutane; 1,5-diaminopentane;1,6-diaminohexane; 1,8-diaminooctane; 1,9-diaminononane;1,10-diaminodecane; 1,12-diaminododecane; 1,4-diaminocyclohexane;2,5-diaminoxylene; and isophoronediamine.

In a preferred embodiment, the elastomeric polymer of the presentinvention the polyisobutylene macrodiol is hydroxyallyl telechelicpolyisobutylene and the hard segment includes a product of a reaction of4,4′-methylenediphenyl diisocyanate and 1,4-butanediol.

In another embodiment, the present invention is an article ofmanufacture comprising any of the polyurethane elastomeric compositionsdescribed above. In preferred embodiments, the article is a medicaldevice or an implant. Examples of the article of the present inventioninclude a cardiac pacemaker, a defibrillator, a catheter, an implantableprosthesis, a cardiac assist device, an artificial organ, a pacemakerlead, a defibrillator lead, a blood pump, a balloon pump, anarteriovenus shunt, a biosensor, a membrane for cell encapsulation, adrug delivery device, a wound dressing, an artificial joint, anorthopedic implant or a soft tissue replacement. In other embodiments,the article is a fiber, film, engineering plastic, fabric, coating, oradhesive joint.

The methods of synthesis of polyurethane compositions are generally wellknown by one of ordinary skill in the art of polymer chemistry. See, forexample, Gunter Oertel, “Polyurethane Handbook”, 2nd ed. HanserPublishers (1993); or Malcolm P. Stevens, “Polymer Chemistry”, 3d ed.Oxford University Press (1999). The relevant portions of thesepublications are incorporated herein by reference.

The present invention is based, in part, on the discovery of new andimproved methods of polyurethane synthesis. In an example embodiment,the present invention is a method of forming a polyisobutylene-basedthermoplastic, comprising the steps of (a) reacting a polyisobutylenemacrodiol and/or diamine with a diisocyanate to form a first reactionmixture; (b) combining a metal catalyst and a chain extender with thefirst reaction mixture to create a second reaction mixture, a molarratio of the metal catalyst to the diisocyanate being greater than 0.0:1and less than or equal to 0.4:1; and (c) reacting the second reactionmixture for a period of time sufficient to form thepolyisobutylene-based thermoplastic urethane.

In another embodiment, the polyisobutylene-based thermoplastic urethaneresulting from the above method comprises (1) a hard segment in theamount of 10% to 60% by weight of the elastomeric polymer, wherein thehard segment includes a urethane, urea or urethaneurea; and (2) a softsegment in the amount of 40% to 90% by weight of the elastomericpolymer, wherein the soft segment includes a polyisobutylene macrodioland/or diamine and does not include a polyether macrodiol.

Preferably, the polyisobutylene-based thermoplastic urethane includes ahard segment with a polydiversity index greater than or equal to 1.58and less than or equal to 2.17.

In the present invention, a catalyst may be present in the secondreaction mixture, such as stannous octoate (Sn(oct)₂). Other catalystsare well known in the art and can be used by one of the ordinary skillin the art.

Any one or more of the isocyanates, chain extenders, or variousadditives can be employed with the synthetic method of the presentinvention. Any amounts of the components and their combinationsdescribed above can be used.

In an example embodiment, the present invention relates topolyisobutylene-based thermoplastic urethanes, formed by a methodcomprising the steps of (a) reacting a polyisobutylene diol with adiisocyanate to form a reaction mixture; (b) combining a metal-catalystof an alkyl diol with the reaction mixture, a molar ratio x of elementalmetal of the metal-catalyst to diisocyanate being in a range of0.0:1<x<0.4:1; and (c) reacting the reaction mixture with themetal-catalyst of alkyl diol for a period of time sufficient to form thepolyisobutylene-based thermoplastic urethane.

EXEMPLIFICATION Materials

4,4′-Methylenebis(phenyl isocyanate) (MDI) (98%), 1,4-butandiol (BDO)(99%), Tin(II) 2-ethylhexanoate (Sn(oct)₂) (95%), KMnO₄, chloroform (atleast 99.8%), LiBr (Lithium bromide at least 99%), KOH (potassiumhydroxide), Na₂SO₄ (sodium sulfate), Trifluoroacetic acid (TFA), andtoluene (>99.5%) were purchased from Sigma-Aldrich.Tetra-n-butylammonium bromide (TBAB, at least 98%) was purchased fromAlfa Aesar. Toluene was dried over sodium metal and distilled.Tetrahydrofuran (THF) was refluxed over sodium metal and benzophenoneover night and distilled under nitrogen atmosphere prior to use. Hexaneswere purified by refluxing over sulfuric acid for 24 hours. They werewashed with aqueous solution of KOH three times followed by distilledwater. Then they were stored over sodium sulfate over night at roomtemperature. Finally they were distilled over CaH₂ under nitrogenatmosphere before use. BDO was dried at 70° C. under vacuum before use.All the other chemicals were used as received.

Instrumentation

Gel permeation chromatography (GPC) was measured on a Waters systemequipped with a model 510 HPLC pump, model 410 differentialrefractometer, model 441 absorbance detector and online multiangle laserlight scattering detector. Tetrahydrofuran (THF) containing 2 wt %tetra-n-butylammonium bromide (TBAB) was used as the flow phase, and theflow rate was 1 mL/min.

Differential scanning calorimetry (DSC) was performed on a TA InstrumentQ100 instrument equipped with a refrigerated cooling system and nitrogenpurge (50 mL/min). About 5-10 mg of sample was sealed in an aluminum panand heated or cooled at a rate of 10° C./min. To minimize the effects ofthermal history, the samples were cycled at a rate 10° C./min between−80° C. and 240° C.

Dynamic mechanical analysis (DMA) was performed on a TA Instruments Q800instrument. The TPUs were first compression molded at 180° C. into flatfilms, which were then cut into rectangular thin strips and fixed onto afilm tension clamp and heated from −100° C. to 40° C. at a rate of 2°C./min and a frequency of 1 Hz.

Two-dimensional small angle X-ray scattering (SAXS) was performed atbeamline X27C, National Synchrotron Light Source (NSLS), BrookhavenNational Laboratory (BNL). The wavelength of incident X-ray beam was0.1371 nm, and the sample-to-detector distance was 1789.70 mm. Sampleswere cut from the compression molded films, mounted onto the samplestage and measured in the open air. Scattering signals were collected bya marCCD 2D detector with a resolution of 158 μm/pixel. Typical exposuretime was between 30-90 s. One-dimensional SAXS profiles were obtained byintegration of the corresponding two-dimensional scattering patterns andthe subsequent background subtraction. Absolute scattering intensity wasthen determined using a pre-calibrated glassy carbon secondary standard.

For one-dimensional SAXS profiles, scattering intensity I(q) is plottedas a function of scattering vector q, which is defined as:

$\begin{matrix}{q = {\frac{4\pi}{\lambda}\sin \; \theta}} & (1)\end{matrix}$

Here λ is the wavelength of incident X-ray beam, and 2θ is thescattering angle. If microphase separation is observed, domain spacing dcan be calculated by:

$\begin{matrix}{d = \frac{2\pi}{q_{\max}}} & (2)\end{matrix}$

where q_(max) is the position of the scattering peak.

If the HS and SS in a TPU are completely microphase separated, thetheoretical electron density variance (Δρ)² is defined as:

(Δρ)² =ϕ_(H)ϕ_(S)(ρ_(H)−ρ_(S))²  (3)

Here φ_(H) and φ_(S) correspond to the volume fraction of HS and SS inthe TPU, and ρ_(H) and ρ_(S) are the electron density of the HS and SS,respectively. Electron density of a given compound ρ_(e) can becalculated by

$\begin{matrix}{\rho_{e} = {\rho_{m}\frac{\sum\limits_{i}\; Z_{i}}{\sum\limits_{i}\; A_{i}}}} & (4)\end{matrix}$

Where ρ_(m) is the mass density of the compound, and Z_(i) and A_(i) arethe atom number and atomic weight of each atom in the compound.

The actual electron density variance (Δρ′)² , on the other hand, isrelated to scattering invariant Q according to the followingrelationship:

$\begin{matrix}{\overset{\_}{\left( {\Delta \; \rho^{\prime}} \right)^{2}} = {{cQ} = {c{\int_{0}^{\infty}{{I(q)}q^{2}{dq}}}}}} & (5)\end{matrix}$

and c is a constant:

$\begin{matrix}{c = {\frac{1}{2\pi^{2}i_{e}N_{A}^{2}} = {1.76 \times 10^{- 24}\mspace{14mu} {mol}^{2}\text{/}{cm}^{2}}}} & (6)\end{matrix}$

Here i_(e) is the Thompson's constant for the scattering from oneelectron, with the value of 7.94×10⁻²⁶ cm², and N_(A) is Avogadro'snumber. Therefore, degree of microphase separation can be calculated asfollows:

Degree of microphase separation=(Δρ′)² /(Δρ)²   (7)

Static tensile properties were measured using an Instron Tensile Tester4400R. The TPUs were compression molded into films by using a CarverLaboratory Press Model C at 180° C. and a load of 16000 lbs. Thethickness of the films ranged between 0.2-0.3 mm. Dog-bone specimen werepunched out according to ASTM D412 and pulled in the Instron at anextention rate of 50 mm/min using a 50 lbs load cell.

Example 1: Preparation of PIB(allyl-OH)₂

Br-Allyl-PIB-Allyl-Br (M_(n)=2200, 50 g, 0.023 mol) was dissolved in dryTHF (1 liter) and a solution of KOH (50 g, 0.9 mol) in distilled water(500 mL) was added to it. The mixture was heated for 3 hour at 130° C.in a reactor. The reaction was cooled to room temperature. The THF wasevaporated using a rotary evaporator. Distilled methanol (500 mL) wasadded and the precipitate was allowed to settle down. The precipitatewas further dissolved in hexanes (200 mL) and slowly added to methanol(600 mL). The sticky mass was allowed to settle down. The process wasrepeated two times and the purified polymer was finally dried undervacuum at room temperature for 24 hour. Yield: 99%, GPC-MALLS:M_(n)=2400, polydispersity index (PDI)=1.16.

Example 2: Synthesis of Polyisobutylene-Based Thermoplastic Polyurethane(PIB-TPU) Using PIB(OH)₂

To a 100 mL three-neck round bottom flask equipped with mechanicalstirring and nitrogen purging, 5.20 g PIB(OH)₂ (2.60 mmol) was added anddried under vacuum at 60° C. overnight to remove moisture. After that,20 mL dry toluene was added to dissolve the PIB(OH)₂, and 1.76 g MDI(6.8991 mmol) was added subsequently at room temperature. The mixturewas stirred at 100° C. for 2 h, and then 0.3662 g BDO (4.1691 mmol) and1.1 mg Tin (II) 2-ethylhexanoate (0.0028 mmol) were added. The mixturewas further stirred at 100° C. for 4 h and cooled to room temperature.The polymer was cured at room temperature under nitrogen purging for 1week and then dried at 70° C. under vacuum overnight to remove residualsolvent.

Five PIB-based TPUs were prepared and their characteristics are listedin Table 1. These TPUs were synthesized via the procedure in Example 2using Sn(oct)₂ as the catalyst. For all the TPUs, molecular weight ofthe PIB(OH)₂ is 2000 g/mol, the hard segment (HS) is based on4,4′-methylenebis(phenyl isocyanate) (MDI) and 1,4-butandiol (BDO), andthe weight fraction of soft segment (SS) is 65%. Catalyst concentrationof these TPUs ranges from 1 mol % to 0 mol %, as related to the totalamount of MDI.

TABLE 1 Summary of the characteristics of PIB(OH)₂-based TPUssynthesized using different catalyst concentrations Catalyst w (SS)Concentration M_(n) M_(w) TPU sample (%) (%) (kg/mol) (kg/mol) PDIPIBPU-0Sn 65 0 64.5 102.1 1.58 PIBPU-004Sn 65 0.04 75.0 139.0 1.87PIBPU-01Sn 65 0.1 101.9 220.8 2.17 PIBPU-04Sn 65 0.4 167.5 354.5 1.62PIBPU-1Sn 65 1 103.5 189.7 1.83

Example 3: Synthesis of Polyisobutylene-Based Thermoplastic Polyurethane(PIB-TPU) Using PIB(allyl-OH)₂

TPUs using PIB(allyl-OH)₂ were prepared by a method analogous to thePIB(OH)₂-based TPU synthesis described in Example 2. Table 2 representsthe number average molecular weight and MWD of PIB(allyl-OH)₂ basedTPUs.

TABLE 2 Molecular Weight and MWD of TPUs Synthesized UsingPIB(allyl-OH)₂ Catalyst Concentration M_(n) Run (%) (kg/mol) MWD PSPU-10.04 58.3 1.79 PSPU-2 0.10 96.5 2.25 PSPU-3 0.40 78.0 1.80 PSPU-4 1.0092.0 1.95

Thermal Analysis of PIB(OH)₂-Based TPUs

The thermal properties of the PIB(OH)₂-based TPUs in Table 1 weresubsequently investigated. PIB-TPUs, in most cases, do not have puresoft segment (SS) and hard segment (HS) microphase separation from eachother. Instead, the microphase separated structure of TPU contains asoft phase (SP) and a hard phase (HP), where SP is formed by thedissolution of some HS into the SS, and HP consists of HS that phaseseparates from the SP. Measuring the glass transition temperature of theSP (T_(g) (SP)) reflects the composition of SP and thus the degree ofmicrophase separation. FIG. 1 is a plot that represents the differentialscanning calorimetry (DSC) profiles of the TPUs, measuring heat flow(mW) as a function of temperature. Unfortunately, DSC of these TPUs didnot show clearly T_(g) (SP), so it is not clear if changing the catalystconcentration leads to different degree of microphase separation. TheseDSC results show, however, that none of the samples show melting peak ofthe HS, indicating that catalyst concentration has no effects on HScrystallization.

FIGS. 2A and 2B represent the results of dynamic mechanical analysis(DMA) on the TPU samples from Table 1. FIG. 2A is a plot of the DMAprofiles of loss modulus (E″) as a function of temperature of PIB-basedTPUs. FIG. 2B is a plot of the DMA profiles of tan δ as a function oftemperature of PIB-based TPUs. It is evident that all the samples showT_(g) (SP) much higher than T_(g) of PIB homopolymer. This is inagreement with previous results that microphase separation is incompletein PIB-based TPUs. Table 3 further summarizes the value of T_(g) (SP) ofthese TPUs. As can be seen, all the samples have similar T_(g) (SP),indicating that the degree of microphase separation is not significantlyaffected by catalyst concentration.

TABLE 3 Summary of value of T_(g)(SP) of PIB-based TPUs T_(g)(SP) (° C.)Determined Determined TPU from E″ from tan δ PIBPU-0Sn −40.4 −14.1PIBPU-004Sn −43.4 −20.6 PIBPU-01Sn −44.1 −18.8 PIBPU-04Sn −38.5 −22.2PIBPU-1Sn −42.8 −22.5

FIGS. 3A and 3B represent the results of small angle X-ray scattering(SAXS) on the TPU samples from Table 1. The samples were compressionmolded at 180° C. FIG. 3A is a plot of the SAXS profiles of I as afunction of q for PIB-based TPUs. FIG. 3B is a plot of the SAXS profilesof q²I as a function of q for PIB-based TPU's. Both PIBPU-004Sn andPIBPU-0Sn show two separate scattering peaks, one in the q range of0.35-0.5 nm⁻¹, and the other one around 0.9 nm⁻¹. This result is inagreement with previous observations that two different microphaseseparated structures can be observed in PIB-based TPUs with a certainrange of SS weight fraction. PIBPU-01Sn also shows two scattering peaks,at q=0.76 nm⁻¹ and q=0.54 nm⁻¹, respectively, but the peak at lower qvalue only appears as a weak shoulder. On the other hand, PIBPU-04Sn andPIBPU-1Sn only show one scattering peak in the q range of 0.3-0.4 nm⁻¹,and no additional peak is observed at higher q range. These resultsclearly suggest that catalyst concentration has dramatic effects on themicrophase separated morphology of PIB-based TPUs. It is likely thatincreasing the concentration of Sn(oct)₂ leads to the disappearance ofthe microphase separated structure with smaller domain spacing.

The actual electron density variance (Δρ′)² of these PIB-based TPUs wasthen calculated using eq. (5) and (6). According to literature, lowmolecular weight PIB has a density of 0.913 g/cm³, and density of HSbased on MDI and BDO is reported to be 1.33-1.4 g/cm³. A value of 1.33g/cm³ was used. If the contribution of residual Sn catalyst on X-rayscattering contrast can be neglected, according to eq. (3) and eq. (4),(Δρ)² of these PIB-based TPUs is 6.40×10⁻³ (mol e⁻/cm³)². Therefore,degree of microphase separation of these samples can be calculated viaeq. (7), and the results are summarized in Table 4.

TABLE 4 Summary of domain spacing and degree of microphase separationfor PIB-based TPUs synthesized under different catalyst concentrations(Δρ′)² × Degree of d₁ d₂ 10³((mol Microphase Sample (nm) (nm) e⁻/cm³)²)Separation PIBPU-0Sn 17.0 6.9 3.30 0.52 PIBPU-004Sn 12.3 7.1 3.17 0.49PIBPU-01Sn 11.2  8.27 3.48 0.54 PIBPU-04Sn 15.3 N/A 3.33 0.52 PIBPU-1Sn20.3 N/A 4.12 0.64

It is evident that, all the samples have degree of microphase separationaround 0.5-0.6. This is consistent with previous investigation thatmicrophase separation in PIB-based TPUs is not complete. It is alsoclear that, while varying catalyst concentration results in substantialchange in the domain spacing of these TPUs, it does not affect degree ofmicrophase separation significantly. As can be seen, although PIBPU-1Snhas a much higher degree of microphase separation, about 0.64, all theother four samples have degree of microphase separation around 0.5.

FIGS. 4A and 4B represent results of SAXS after the samples werecompression molded at 180° C., and further annealed at 140° C. for 12 h.FIG. 4A is a plot of the SAXS profiles of I as a function of q forPIB-based TPUs. FIG. 4B is a plot of the SAXS profiles of q²I as afunction of q for PIB-based TPU's. As can be seen from FIGS. 4A, 4B, andTable 5, for most samples the shape of SAXS profiles and value of domainspacing did not change significantly during annealing, although forPIBPU-01Sn, the shoulder peak at q=0.54 nm⁻¹ disappeared afterannealing, and for PIBPU-1Sn, annealing resulted in an decrease indomain spacing. It is also clear that all the TPUs showed a decrease indegree of microphase separation after thermal annealing. This is inagreement with previous results that thermal annealing can promote thephase mixing between the SS and HS. For the annealed samples, degree ofmicrophase separation is also not significantly dependent on catalystconcentration. As can be seen from Table 5, the degree of microphaseseparation slightly increased from 0.41 to 0.48 as the Sn(oct)₂concentration increased from 0 to 0.4 mol %, but it slightly dropped to0.46 as the catalyst concentration further increased to 1 mol %.

TABLE 5 Summary of domain spacing and degree of microphase separationfor PIB-based TPUs synthesized under different catalyst concentrations(Δρ′)² × Degree of d₁ d₂ 10³((mol Microphase Sample (nm) (nm) e⁻/cm³)²)Separation PIBPU-0Sn 17.4 6.8 2.64 0.41 PIBPU-004Sn 12.1 7.3 2.69 0.42PIBPU-01n 11.7 N/A 2.82 0.44 PIBPU-04Sn 15.7 N/A 3.10 0.48 PIBPU-1Sn14.3 N/A 2.94 0.46

FIG. 5 is an illustration that represents example structuralconformations PIB-based TPUs may form based on catalyst concentration.

Mechanical Properties of TPUs

FIG. 6 is a plot representing the stress-strain curves of PIB-based TPUssynthesized using different catalyst concentration. The sample PIBPU-1Sncould not be compression molded into films with good quality. It isclear that, when the TPUs was synthesized using 0.4 mol % of Sn(oct)₂catalyst, tensile strength at break only reached ˜10 MPa, similar toprevious results. However, when the catalyst concentration was decreasedto 0.1 mol % or lower, tensile strength at break significantly increasedto 21 MPa. As catalyst concentration decreased, elongation of break wasalso enhanced, around 350%.

Table 6 describes the tensile strength (UTS) and the percent elongation(UTE) measurements of PIB(OH)₂-based TPUs.

TABLE 6 PIB-Based TPUs Mechanical Properties TPU sample Sn(oct)₂ M_(n)(kg/mol) PDI UTS (MPa) UTE (%) PIBPU-0Sn 0 64.5 1.58 20 233 PIBPU-004Sn0.04% 75.0 2.09 21 ± 1 350 ± 30 PIBPU-01Sn 0.1% 101.9 2.17 21 ± 1 310 ±20 PIBPU-04Sn 0.4% 167.5 1.62 10 ± 1 280 ± 40 PIBPU-1Sn 1.0% 103.5 1.83 9 ± 1 350 ± 50

Oxidation of TPUs

A study of the oxidative stability of PIB(OH)₂-based TPUs andPIB(allyl-OH)₂-based TPUs was performed by subjecting the PIB-based TPUsto KMnO₄ in THF/water at 70° C. for 24 h.

FIG. 7 is a plot that represents results of the size exclusionchromatography (SEC) performed on the PIB(OH)₂-based TPU before andafter attempted oxidation. Table 7 demonstrates that the molecularweight and the MWD of the PIB(OH)₂-based TPU remained unchanged afteroxidation, suggesting that the amide linkage of the TPUs is not affectedduring oxidation.

TABLE 7 GPC data of PIB(OH)₂-based TPU before and after oxidation BeforeOxidation After Oxidation Run M_(n) (kg · mol⁻¹) MWD M_(n) (kg · mol⁻¹)MWD PIB-PUR 158.0 3.10 156.1 2.99

The PIB(allyl-OH)₂-based TPU was subjected to the same oxidativeconditions and oxidized at the C═C double bond. From the cleavedmaterial, the soft segment and hard segment were separated by repeateddissolution and precipitation in hexane and methanol. FIG. 8 is a plotthat represents the results of the SEC performed on PIB(allyl-OH)₂overlaid on top of the results of the SEC performed on the cleaved softsegment. The SEC-RI tract of the soft segment was exactly identical tothe original PIB before TPU synthesis.

FIG. 9 is a plot that represents the SEC-RI of the cleaved hard segmentmeasured in THF using a do/dc value of 0.24 mL/g. Table 8 demonstratesthat as catalyst concentration increased, the MWD of the hard segmentincreased.

TABLE 8 GPC of the hard segment after oxidation of PIB(allyl-OH)₂-basedTPUs Catalyst Concentration MW of HS Run (%) (M_(n)/PDI) PSPU-1 0.040.86k/2.04 PSPU-2 0.10 0.93k/2.29 PSPU-3 0.40 1.08k/2.94 PSPU-4 1.001.15k/3.41

CONCLUSION

In summary, it has been shown that catalyst concentration hassignificant effects on the morphology and mechanical properties ofPIB-based TPUs. While the PIB-based TPUs synthesized at differentcatalyst concentrations have similar degree of microphase separation,varying the catalyst concentration leads to substantial changes indomain spacing. Strikingly, the mechanical properties of PIB-based TPUscan be significantly improved by lowering the catalyst concentration.This is attributed to the narrower MWD of the hard segments upondecreasing the catalyst concentration. These results may help preparePIB based TPUs with both high mechanical strength and excellentbiostability.

EQUIVALENTS

The teachings of all patents, published applications and referencescited herein are incorporated by reference in their entirety.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method of forming a polyisobutylene-basedthermoplastic urethane, comprising the steps of: a) reacting apolyisobutylene macrodiol and/or diamine with a diisocyanate to form afirst reaction mixture; b) combining a metal catalyst and a chainextender with the first reaction mixture to create a second reactionmixture, a molar ratio of the metal catalyst to the diisocyanate beinggreater than 0.0:1 and less than or equal to 0.001:1; and c) reactingthe second reaction mixture for a period of time sufficient to form thepolyisobutylene-based thermoplastic urethane.
 2. The method of claim 1,wherein the polyisobutylene-based thermoplastic urethane comprises: (1)a hard segment in the amount of 10% to 60% by weight of thepolyisobutylene-based thermoplastic urethane, wherein the hard segmentincludes a urethane; and (2) a soft segment in the amount of 40% to 90%by weight of the polyisobutylene-based thermoplastic urethane, whereinthe soft segment includes the polyisobutylene macrodiol and/or diamine;wherein the number average molecular weight of the polyisobutylene-basedthermoplastic urethane greater than or equal to about 40 kilodaltons;wherein the polydispersity index of the elastomeric polymer is between1.58 and 2.17, inclusive; and wherein the soft segment does not includea polyether macrodiol.
 3. The method of claim 1, wherein the firstreaction mixture consists essentially of a polyisobutylene macrodioland/or diamine and a diisocyanate.
 4. The method of claim 2, wherein thenumber weight molecular average of the polyisobutylene-basedthermoplastic urethane is greater than or equal to 50 kilodaltons. 5.The method of claim 2, wherein the polyisobutylene macrodiol or diamineis of the formula:

wherein: each X is independently —OH, —NH₂, or —NHR₄; R₁ is an initiatorresidue; R₂, R₃, and R₄ is, each independently, a C₁-C₁₆ alkyl, a C₃-C₁₆cycloalkyl, a C₂-C₁₆ alkenyl, a C₃-C₁₆ cycloalkenyl, a C₂-C₁₆ alkynyl, aC₃-C₁₆ cycloalkynyl, or a C₆-C₁₈ aryl, wherein, for each occurrence, R₂or R₃ is, independently, optionally substituted with one or more groupsselected from halo, cyano, nitro, dialkylamino, trialkylamino, C₁-C₁₆alkoxy, and C₁-C₁₆ haloalkyl; and n and m are each, independently,integers from 1 to
 500. 6. The method of claim 2, wherein the hardsegment is present in the amount of from about 30% to about 50% byweight of the elastomeric polymer.
 7. The method of claim 1, wherein thepolyisobutylene macrodiol is hydroxyallyl telechelic polyisobutylene. 8.The method of claim 1, wherein the polyisobutylene macrodiol ishydroxyalkyl telechelic polyisobutylene.
 9. The method of claim 8,wherein the polyisobutylene macrodiol is hydroxypropyl telechelicpolyisobutylene.
 10. The method of claim 1, wherein the polyisobutylenemacrodiamine is aminoallyl telechelic polyisobutylene.
 11. The method ofclaim 18, wherein the number average molecular weight of thepolyisobutylene macrodiol is about 400 Da to about 6000 Da.
 12. Themethod of claim 1, wherein the number average molecular weight of thepolyisobutylene macrodiol is about 1000 Da to about 3000 Da.
 13. Themethod of claim 1, wherein the diisocyanate includes at least one memberselected from the group consisting of 4,4′-methylenephenyl diisocyanate;methylene diisocyanate; p-phenylene diisocyanate;cis-cyclohexane-1,4-diisocyanate; trans-cyclohexane-1,4-diisocyanate; amixture of cis-cyclohexane-1,4-diisocyanate andtrans-cyclohexane-1,4-diisocyanate; 1,6-hexamethylene diisocyanate;2,4-toluene diisocyanate; cis-2,4-toluene diisocyanate;trans-2,4-toluene diisocyanate; a mixture of cis-2,4-toluenediisocyanate and trans-2,4-toluene diisocyanate; p-tetramethylxylenediisocyanate; and m-tetramethylxylene diisocyanate.
 14. The method ofclaim 1, wherein the chain extender is selected from the groupconsisting of a C2-C12 alkyl diol and a C2-C12 alkyl diamine.
 15. Themethod of claim 14, wherein the chain extender is a C2-C6 alkyl diol.16. The method of claim 1, wherein the chain extender includes at leastone member selected from the group consisting 1,4-bunatediol;1,5-pentanediol; 1,6-hexanediol; 1,8-octanediol; 1,9-nonanediol;1,10-decanediol; 1,12-dodecanediol; 1,4-cyclohexane dimethanol;p-xyleneglycol; and 1,4-bis(2-hydroxyethoxy)benzene.
 17. The method ofclaim 1, wherein the chain extender includes at least one memberselected from the group consisting of 1,4-diaminobutane;1,5-diaminopentane; 1,6-diaminohexane; 1,8-diaminooctane;1,9-diaminononane; 1,10-diaminodecane; 1,12-diaminododecane;1,4-diaminocyclohexane; 2,5-diaminoxylene; and isophoronediamine. 18.The method of claim 1, wherein the diisocyanate is 4,4′-methylenephenyldiisocyanate and wherein the chain extender is 1,4-butanediol.
 19. Themethod of claim 1, wherein: the polyisobutylene macrodiol ishydroxyallyl telechelic polyisobutylene; the diisocyanate is4,4′-methylenephenyl diisocyanate; and the chain extender is1,4-butanediol.
 20. A method of forming a polyisobutylene-basedthermoplastic urethane, comprising the steps of: a) reacting apolyisobutylene diol with a diisocyanate to form a reaction mixture; b)combining a metal-catalyst of an alkyl diol with the reaction mixture, amolar ratio x of elemental metal of the metal-catalyst to diisocyanatebeing in a range of greater than 0.0:1 and equal to or less than0.001:1; and c) reacting the mixture with the metal catalyst of alkyldiol for a period of time sufficient to form the polyisobutylene-basedthermoplastic urethane.
 21. A method of claim 20, wherein thepolyisobutylene diol has the structural formula:

wherein n is a number in a range between about 5 and about
 200. 22. Themethod of claim 21, wherein the diisocyanate is methylenebis(phenylisocyanate).
 23. The method of claim 22, wherein the alkyldiol is 1,4-butanediol.
 24. The method of claim 23, wherein the metalcatalyst is Tin(II) 2-ethylhexanoate.
 25. The method of claim 1, whereinthe molar ratio of the metal catalyst to the diisocyanate is equal to0.001:1.
 26. The method of claim 1, wherein the motor ratio of thediisocyanate is equal to 0.0004:1.
 27. The method claim 21, wherein themolar ratio of metal catalyst to the diisocyanate is equal to 0.001:1.28. The method of claim 21, wherein the molar ratio of metal catalyst tothe diisocyanate is equal to 0.0004:1.